I can take a swing at your questions.
According to the EIA, the total CO2 emissions in the US for 2005 is 5,909 million metric tons, 2,136 MMT from coal, 2,585 MMT from petroleum, and 1,175 MMT from natural. From the same source, global CO2 emissions were 21,162 MMTCO2 (in 2003).
From:
http://www.strom.clemson.edu/becker/...s/carbon3.html
Quote:
Anthropogenic carbon emissions per year has reached a troublesome magnitude. Today, the atmosphere contains about 720 Gtons of carbon. The concentration of carbon dioxide is about 360 ppm. Regardless of its source, one billion tons of carbon released into the atmosphere as carbon dioxide would increase its concentration by 0.5 ppm (360 / 720) if all of it stayed there. However, scientists estimate that about half of present human carbon emissions are absorbed by the environment. Of the half absorbed, scientists have accounted for where half of that goes. Where the other half goes is the "mystery of the missing carbon" (about 1.8 Gton per year).
Since about half of human carbon emissions are not absorbed by the environment, this fraction accumulates in the atmosphere from year to year. A better way to look at the relation between carbon emissions and atmospheric carbon dioxide concentration is to examine the cumulative total of emissions. These data are shown in Figure 2. They have been fitted with a linear regression (i.e., best linear fit) from the year 1900 to present. The slope of the relation is 0.266 ppm per year per Gton of emissions. If exactly half of human carbon emissions have been absorbed by the environment, the slope would be 0.25 (0.5 / 2). The expected intercept is 298 ppm (in the year 1900). That of the regression is 293. The r-square goodness of fit is 0.996. This means that 99.6% of the variance (i.e., variability) in atmospheric carbon dioxide concentration is completely accounted for by anthropogenic carbon emissions. The correlation coefficient between cumulative anthropogenic carbon emissions and atmospheric carbon dioxide concentration is r = 0.998 (e.g., r = 1.0 represents an absolutely perfect match).
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It is estimated that human activities spew 150 times the CO2 into the atmosphere compared to volcanoes.
http://volcano.und.edu/vwdocs/Gases/man.html
The amount of CO2 trapped by landfills, septic systems, buried corpses, etc. is negligible. But CO2 is only one of a number of greenhouse gases.
Water vapor traps heat. So does methane, which is 21 times more potent an infrared-absorbing agent compared to CO2. Methane levels currently are at the highest concentration in the atmosphere in the last 400,000 years (based on air bubbles trapped in Antarctic ice).
You can get all the skinny you want by doing web searches. Wiki has a good article at:
http://en.wikipedia.org/wiki/Greenhouse_gas
Though the ins and outs may be debated, there is really no argument that since the Industrial Revolution atmospheric CO2 levels have increased more than 25 percent.
Hope that helps....